Depends how desperate you are.

Steps:

  1. Clone your Shapes
  2. Add Shapes
  3. Colour Shape
  4. Break Shapes - the intersection space is now filled
  5. Move Shape behind.

As it does not depend on any adjustments, this could be set as a Macro.
If you reposition the initial Shapes, you need to repeat the steps.

I use AutoHotKeys.
Xara needs to introduce its own macro recorder.

Acorn